BIOL 240W 1st Edition Lecture 10 Outline of Last Lecture I. Pull of Water and Nutrients Due to TranspirationII. Bulk Flow vs. DiffusionIII. StomataIV. Transport of SugarsV. Phloem as an “Information Superhighway”Outline of Current Lecture I. General Characteristics of TransportII. OsmosisIII. Water PotentialIV. Long Distance Transport - Bulk FlowV. Transport Through PhloemCurrent LectureI. General Characteristics of Transporta. Transport in a plant depends on a change or difference in pressure/water potential. This is why dead cells have the ability to carry out these processesb. Cells in the phloem must be living to carry out the co-transport of sugars.c. Materials moving from one cell to the nexti. Apoplastic route moves through cell walls and spaces between cells, xylem elementsii. Symplastic route moves things to be transported through living parts of the cell (cytoplasm). There are connections between each cell called the plasmodesmata.iii. Transmembrane is problematic, but third option to go through multiple plasma membranesd. Plasma membrane is selectively permeable and plays a role in short distance cell-cell transport.e. Cells use membrane potential to set up a difference in charges (voltage) due to differential distribution of ions on one side of membrane compared to the otheri. Plant can use cell as a battery (take advantage of voltage)ii. Use of ATP to pump protons to create buildup of charged particles. Cell uses this to drag sucrose into the cell because sucrose cannot enter the cell on its ownThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.II. Osmosisa. Movement of free water (it is not bound to any other molecules) in and out of cell b. Dependent on solute concentration and pressure that is involvedc. Free water moves from high concentration of water to low concentration of water. Selectively permeable membrane allows water to move instead of solute.d. Same solute concentration on either side is the end result, but it is because of water movementIII. Water potentiala. Movement of one side of gradient to another. This determines direction of water movement. b. Water flows from regions of higher water potential to regions of lower water potential. Plant can use water potential difference to perform workc. Solute potential + pressure potential = water potentiald. Solute potential depends on molarityi. Decreases with addition of solutesii. Pure water = solute potential of zeroiii. Solutes bind to water molecules and reduce its ability to move and do workiv. Do not need to know numbers/ mathematical problems with water potentiale. Pressure potential is physical pressure on a solutioni. Can be positive/negative. Water in living cells is under positive pressure normally ii. Turgor pressure- pressure exerted by protoplast against cell wall1. Protoplast is the living part of the cell, including the plasma membrane2. Stomata and turgor pressure are directly relatedf. Hypotonic- solution surrounding cell that will cause the cell to take up waterg. Isotonic- solution surrounding a cell that will cause no net movement of water into or outh. Hypertonic- solutions surrounding the cell that will cause a net movement of water out of the celli. Plant cells function in hypotonic solution because rigid cell wall gets pushed back, causing the healthy plant to be stiff from turgor pressurei. Watering plants reverses wiltingj. Plasmolysis is the shrinkage of cytoplasm and detachment of plasma membrane from cell wall in hypertonic solutionk. It is important that there is enough water in cells to keep them turgid. Ideally, turgor pressure pushes against cell wall to prevent wilting.IV. Long Distance Transport- Bulk Flowa. Dependent upon pressure gradient- still moves high to low pressureb. Solute concentration does not have an effectc. Transpirationi. Plants need water for photosynthesis. Evaporating water creates a “pull” upwardfor water, but too much water loss is detrimentalii. Moving water from soil into roots moves through apoplastic route, but must enter xylem through casparian strip1. Casparian strip is limiting. Water must exit apoplastic route to move pastcasparian stripiii. How does the water get there?1. Root pressure is a minimal contributing factor. Even though this is positive pressure, it is too weak to overcome gravity over the long distance. Must rely on transpiration2. What is pulling water up xylem?a. Outside of plant is drier than what is inside. This creates a difference in water potential. Plant takes advantage of this gradient by moving water up to the leaves (down water potential gradient) b. Adhesion- force between water molecules and other things inside xylemc. Cohesion- attractive force between water molecules themselves. d. Surface tension- tension has a negative pressure potential “sucking” of wateriv. Water moving out must be replacedv. During a drought or freezing, there is a break down of cohesive forces that create an air pocket. Plants can adapt and detour around thisvi. Stomata- movement of potassium in cell makes turgid guard cells around stoma.This opens the stoma.V. Transport through Phloema. How do sugars move through plant?i. Transported through phloem by translocationii. Source-net produceriii. Sink- consumer/storage site1. At some other time/season, these roles / differences in need for plant changes role2. No matter the change in roles, sugars always move source sinkb. Sugars cannot move through membrane themselves so energy is needed (hence, the need for living cells)i. Proton pumps make a gradient to move sugars against concentration gradientc. Pressure flow hypothesis for phloem movementi. How do we move source sink?1. There is a lower concentration of sucrose in the source cell than present in phloem. This is where co-transport occurs2. Sucrose of source cell is moved into phloem and changes the water potential3. Sucrose moves through phloem to positive pressure (toward sink)4. Once sucrose reaches the sink, sugars are unloaded and water is recycled from phloem back to
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